1. Field
The invention relates to the field of wax emulsions and mixtures for addition to settable gypsum formulations and other construction and building formulations, and more particularly to the field of such mixtures and emulsions for making gypsum wallboards having low water absorption.
2. Description of the Related Art
Gypsum wallboard is used to form interior and exterior walls of buildings. Standard gypsum wallboard is made by preparing a gypsum slurry, positioning the slurry between two liners and allowing it to set. Standard wallboard formulations are not water resistant and lose strength when exposed to water. Furthermore, mildew, mold, or other biological growth can contaminate the wallboard if it is exposed to water.
Multiple attempts have been made to increase the water resistance of gypsum wallboard. One method includes adding an emulsion containing various compounds such as waxes, saponifying agents, emulsifiers, and other additives such as asphalt to a gypsum slurry.
U.S. Pat. No. 3,935,021 discloses adding an asphalt/wax emulsion with polyvinyl alcohol to a gypsum slurry to impart water-resistant properties. The asphalt/wax emulsion may include paraffin or microcrystalline wax in a ratio of about 1 part wax to 3 parts asphalt.
U.S. Pat. No. 4,094,694 discloses an asphalt/wax emulsion with polyvinyl alcohol and a borate compound added to a gypsum slurry to improve water-resistance. The wax may include paraffin or montan wax. U.S. Pat. No. 5,397,631 also describes an asphalt/wax emulsion with polyvinyl alcohol added to a gypsum slurry for improving the water-resistant properties. After the wallboard is formed, a coating of resin latex is added to further improve the water-resistant characteristics of the wallboard.
U.S. Pat. No. 5,437,722 describes a water-resistant gypsum composition and asphalt-free wax emulsion that includes a paraffinic hydrocarbon having a melting point of about 40° C. to 80° C., about 1 to 200 parts by weight montan wax per 100 parts of the paraffinic hydrocarbon, and about 1 to 50 parts by weight polyvinyl alcohol per 100 parts of the paraffinic hydrocarbon. Aqueous wax emulsions shown to be effective for improving the water-resistant properties of gypsum wallboard are also commercially available. One such commercial prior art aqueous emulsion is Aqualite® 70 provided by Henry Company, El Segundo, Calif. This emulsion has been shown to be very effective for increasing the moisture resistance of gypsum wallboard.
US Patent Publication No. 2010-0116406 A1 also teaches use of a synthetic montan-based formulation for use in water-resistant gypsum wallboard. Other effective commercial wax-based emulsions for use in gypsum wallboard include Aqualite® 30, Aqualite® 700 and Aqualite® 800 which are also provided by Henry Company.
While water-resistance can be achieved with the various emulsions described above, it would be desirable to achieve improved water resistant properties of gypsum wallboard, while lowering the cost of preparing such emulsions. Accordingly, there is a need in the art for compositions and methods that improve the water resistant properties of gypsum wallboard while reducing the costs of making such emulsions, particularly with respect to raw material costs.